ESA’s CryoSat and the Copernicus Sentinel-1 missions have been used to measure subtle changes in the elevation and flow of ice shelves that, in turn, reveals how huge canyons are forming underneath. Warm bottom ocean water is entering the cavity under Antarctica’s Dotson ice shelf and is stirred by Earth’s rotation. This is causing one side of the ice shelf to melt. The canyon, which has formed over 25 years, is now 200 m deep in places and the ice just above it is heavily crevassed, affecting the shelf’s future ability to buttress the ice on land.